1. Field of the Invention
The present invention relates to an apparatus for measuring an ionic concentration in a sample and more particularly to a compact instrument for measuring an ionic concentration having a sheet-type electrode capable of simultaneous measurement of different ions.
2. Description of Related Art
Apparatus for measuring an ionic concentration in a liquid, such as sample solutions, have used so-called sheet-type electrodes for the measurement of ions with an ion selective electrode and a reference electrode formed on the same sheet. With a sheet-type electrode, a measurement of an ionic concentration is possible by the use of a remarkably small quantity of a liquid sample, such as 100 .mu.l to 1 m l. As a result numerous instruments have been widely used for the measurement of an ionic concentration in various kinds of liquids, including blood.
However, the conventional sheet-type electrode for use in a measurement of ions can measure an ionic concentration of only a single ion and thus it has been necessary in order to provide for the simultaneous measurement of a plurality of kinds of ions that a plurality of sheet-type electrodes for use in the measurement of ions are prepared to carry out an individual measurement. Accordingly, problems have occurred, for example, a liquid to be tested must be individually prepared for every ion to be measured and it is necessary to repeat the measuring operation for each sheet-type electrode for use in a measurement of ions. Thus, the measurement cycle takes excessive time and it is necessary to prepare additional samples of liquid to be tested. Additionally, separate testing procedures can introduce errors, since conditions could vary between each procedure.